Abstract: This paper presents design, modeling and simulation of Unified power quality conditioner system to improve the power quality. Unified power quality conditioner consists of combined series and shunt active power filters for simultaneous compensation of voltage and current. The Unified power quality conditioner system is modeled using the elements of Simulink and it is simulated using MATLAB.A new synchronous-reference- frame based control method and d-q-0 theory is used to improve the power quality at the point of common coupling on power distribution systems under unbalanced and distorted load conditions. The results are analyzed and presented using MATLAB simulink software.

Keywords: Active Power Filter (APF), PhaseLockedLoop (PLL), Power Quality (PQ), Synchronous ReferenceFrame (SRF), Unified Power-Quality Conditioner (UPQC).